Options of a PushSubscription

When a pushsubscriptionchange event occurs, it's an opportunity for a developer
to re-subscribe the user for push. One of the pain points of this is that to
re-subscribe a user, the developer has to keep the applicationServerKey (and any
other subscribe() options) in sync between the web page's JavaScript and their
service worker.

In Chrome 54 and later you can now access the options via the options parameter
in a subscription object, known as
PushSubscriptionOptions.

You can copy and paste the following code snippet into
simple-push-demo to see what
the options look like. The code simply gets the current subscription and prints
out subscription.options.